1. I need to cut out a square hole in my console to fit in a Garmin fish finder. Can you give me some tip(s) about cutting into the shiny new fibreglass console. I would like to end up with a smooth cut out but need advice on what to use.
2. Also to mount the fishfinder, the two screws to which the bracket usually fixes need to be removed. I have tried unscrewing them but they don't unscrew all the way. Should I force them?
Any ideas gratefully received.

Mark out the size of the whole required on masking tape, then drill out the corners to make them nice and round,then using a jigsaw with a fibre glass cutting blade (also used for cutting ceramic tiles ) cut neatly and slowly between the drill holes,

Perfect every time.

Also the Garmin screws should just unwind they are useally tight for the last few threads

Ohhh, cutting holes....nightmare. My tip would be to get a sheet of clear plastic, the sort they use on the covers of presentation folders (paper or cardboard will do). Make a template and offer the unit to this to make sure you have your dimensions correct.
Use this as the template on the dash moving it around to find the best location. Once you think you've found the spot check there's enough room behind the dash to take the body of the unit leaving room for wires etc and mark it with a felt pen.
I find laying masking tape over the cutting area also helps leave a very clean cut, however, once the unit is in place you won't see the hole.
Finaly - step away, have a cup of tea and stare at your work area for a good 10 minutes before you drill. Go over and over in your mind what you are about to do and why. You never know, you may just realise you've forgotten to factor something in !!! Good Luck.

__________________Buy it & Use it, then sell it and buy something bigger

Have to agree with MeMe take your time and make up a template before you cut the hole, i cut a hatch hole in the front of my consoul and someone suggested making a template, as it happens the guy i got the hatch off supplied me with a 1/4 inch marine ply template made up for that size hatch, which the hatch fitted perfectly into, i simply found the centre and offered up the template and drew around the inside then stood back and made sure it was in the middle and the correct place.
Then drilled some holes and carefully cut out the shape with a jigsaw, placed the hatch in and drilled through the pilot holes for the screws, the hatch was bedded into a nice bed of sikaflex and secured with self tappers to the consoul, worked a treat and looks great !!

Now when i came to cut out switch panels in the front of the consoul that was a different matter, after a massive battle with the steering wheel trying to get it off i gave up, and instead had to cut out the holes working through and around the wheel, this involved chasing the hole out with a drill and once i'd formed a hole cutting and filling the hole out to shape, took a bit of time but worked out ok and again as someone else said once the lip of the switch is bedded down you dont see the rough edges anyway.